The present invention relates to the field of photography and, more specifically, to photographic apparatus such as autofocusing cameras employing sonic ranging systems for measuring subject distance.
Highly-automated, self-developing cameras of this type are marketed presently by Polaroid Corporation, Cambridge, Massachusetts, under the model designations SX-70 Autofocus and Pronto! Autofocus Land Cameras. For representative examples of these cameras in the patent literature, see commonly-assigned U.S. Pat. Nos. 4,156,567 and 4,168,895.
The sonic ranging system is powered by a flat battery in the film pack and, upon energization, emits a burst of ultrasonic frequency (50-65 khz) from a sonic transducer towards the subject. Thereafter, the same transducer, acting as a microphone, detects an echo signal reflected back from the subject. The time interval between transmission and echo detection is directly proportional to twice the distance to the subject and this measurement is used to provide a ranging signal indicative of subject distance. In turn, the ranging signal is used to control a lens drive system for setting the lens at a corresponding focus position. Representative examples of such a ranging system and a transducer suitable for use therein may be found in commonly assigned U.S. Pat. Nos. 4,199,246 and 4,085,297.
For flash mode operation, cameras of this type may be configured to receive a flashbar (an array of flashbulbs) or an accessory strobe. Alternatively, the strobe may be built into the camera housing. The battery in the camera film pack is used to fire the flashbulbs or strobe unit and in some embodiments is also employed to charge the capacitor in the strobe unit.
To prevent waste of film and/or flashbulbs, certain component status sensing and operating cycle inhibiting circuits are built into these cameras.
For example, commonly-assigned U.S. Pat. No. 4,005,449 discloses a system for automatically inhibiting actuation of the exposure cycle when all of the flash units in the forwardly facing array have been expended thereby preventing waste of a film unit. This system additionally provides a perceptible warning signal (lamp or LED next to the viewfinder) apprising the operator of the expended status of the flash array.
Also see commonly-assigned U.S. Pat. No. 4,064,519 where commencement of the exposure cycle is automatically inhibited if the strobe unit is not turned on, or its capacitor is not fully charged, or if all of the lamps in the flash array are expended. This inhibit system also triggers an operator warning circuit.
Commonly-assigned U.S. Pat. No. 3,774,516 provides a system which is responsive to rotation of the film counter to its "empty" position for inhibiting operation of the flash system when there is no more film in the pack, thereby preventing waste of a flashbulb.
There are numerous conditions--empty film pack, all bulbs expended, strobe off, strobe not fully charged, etc.--that will cause an automatic inhibit of at least part of the camera's operating cycle until the camera operator makes the appropriate correction. To aid the operator, some of these camera systems provide some type of warning signal, usually visual in nature, to indicate the source of the problem.
In autofocusing cameras which include a sonic ranging system, and, additionally, may include several of the inhibit systems previously described, there is a need for quickly and clearly advising the operator as to which condition is causing the inhibit so that he or she may take the appropriate corrective action without having to check all of the possible causes.
Visual information and warning systems are commonly employed in automatic cameras, usually in the form of a multi image display about the periphery of the viewfinder for indicating scene lighting conditions, selected aperture, shutter speed and to warn that the strobe is not fully charged, all flashlamps expended, etc. It would seem that the addition of more visual warning indicators within or around the viewfinder area may be more confusing than helpful to the operator. On the other hand, an audible warning system may be preferable for separating picture taking information provided visually and indicating that the camera is in a ready condition from audible warnings that say something is wrong and corrective action must be taken.
In the past, audible warning systems have been incorporated into self-developing cameras in conjunction with timing circuits that are used to time the imbibition interval for peel apart self-developing film units. For example, see commonly-assigned U.S. Pat. No. 3,608,454 and copending application U.S. Ser. No. 152,858 filed on May 23, 1980, wherein one or more sonic transducers mounted on the camera housing are electrically driven in the audio frequency range to emit an audible warning tone at the end of the timed cycle.
Of necessity, these transducers are quite large in size and the addition of this component to a camera already having a transducer employed in the sonic ranging system would tend to increase the overall size of the camera and be counter-productive in meeting design goals to minimize camera size.
Therefore, it is an object of the present invention to incorporate an audible information system into a camera of the type that includes a sonic ranging system without significantly increasing the size of the camera.
It is another object of the invention to provide such a camera with an audio information system which utilizes at least some of the components forming part of the sonic ranging system to minimize camera complexity and manufacturing costs.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.